The Design And Application Of A Strength Training Machine For Hamstring

Purposes: Hamstring strains are common injuries in sports, especially during sprinting. Through the analysis of the mechanisms of hamstring injury in running, the purpose of this study was to design a specific training machine for hamstring, and to test the effects of 6 weeks'strength training program on knee joint strength as well as sEMG during strength test.Methods: 12 male subjects with no history of hamstring injury completed the training on the designed machine, 3×7 repetitions-3 times a week for six consecutive weeks. Subjects were divided into two groups:"Separate Group"and"Conbined Group". The Separate Group performed forward-falling and leg curl separately. In the Conbined Group, Each repetition involved an eccentric forward-falling and a concentric leg curl in rapid consequence. Isometric and isokinetic strength were tested pre and post training. The sEMG of low extremity muscles were also recorded while strength testing. Results were compared within (pre and post) and between the groups.Results: The comparison of results showed a significant increase in maximal isometric torque of hamstrings and qudriceps at knee position toward full extension but not flexion. Both concentric and eccentric peak torque increased in hamstrings whereas only the eccentric PT at 60°/s went up in quadriceps. No differences were found in iEMG of quadriceps after training while iEMG of lateral hamstring and medial grastrocnemius rised in Separate Group, but not Conbined Group. The iEMG of medial hamstring kept stable in two groups. The CAR(VM/MH) (coactivation rate)increased significantly after training while quadriceps contraction actively, whereas no differences were found in CAR(VM/LH) . In comparison, the CAR(MH/VM) increased significantly in Conbined Group but not Separate Group. The CAR(LH/VM) rised in both groups after training.Conclusions: The designed machine may provide the athletes'neuromuscular system, especially hamstrings, an opportunity to adapt to the training load as well as the mode which is analogous with the hamstring muscle action during sprinting. The results suggest that 6 weeks of hamstrings'strength training is sufficient to improve the muscular strength which is beneficial for injury prevention. Different training mode may lead to varied adaption in hamstring muscles. The amount of antagonist coactivation was prone to decline in the Conbined Group.